Generally, the vehicle such as an automobile is equipped with the airbag device which inflates and develops the airbag therein in such an emergency as collision to restrain the occupant. Various types of the airbag device including the airbag device for driver's seat, which is installed in the steering wheel, the passenger airbag device installed in the instrument panel, the side airbag device installed in the side surface of the vehicle or the seat, the knee airbag device installed in the lower portion of the dash board and the like have been developed and employed. Normally, the airbag device of the aforementioned type is stored in the vehicle part so as not to be noticed by the passenger in the normal state, and is structured to inflate and develop the airbag toward the vehicle interior by breaking the vehicle part in the emergency. The opening of the airbag is required to be covered so as to be assimilated into the vehicle interior surface. Meanwhile, the airbag is required to be ready for smoothly and rapidly inflating/developing in the emergency.
The aforementioned airbag device includes an airbag folded in the normal state so as to be inflated/developed in an emergency, an inflator which supplies gas to the airbag, a retainer which stores the airbag, and an airbag cover which forms the vehicle interior surface in engagement with the retainer. The airbag cover is a thin resin molded plate having a groove called tear line formed in the back surface. The tear line is a groove as a thin portion through which the airbag easily breaks the airbag cover. The door member formed by breaking the airbag cover is turnably held by the hinge portion of the airbag cover to form the opening through which the airbag inflates and develops.
The airbag cover which is integrally resin molded with the inner case for forming the inflation/development path of the airbag on the back surface has been disclosed (for example, see Japanese Unexamined Patent Application Publication No. 2007-290409). The airbag cover disclosed in Japanese Unexamined Patent Application Publication No. 2007-290409 has the protruding leg piece on the back surface of the non-development portion other than the hinge portion, and has the proximal end portion provided with the first thin portion with small thickness in order to prevent generation of the sink (deformation caused by shrinkage upon resin curing) in the airbag cover surface during manufacturing when the leg piece of the inner case is thick.
The airbag cover disclosed in Japanese Unexamined Patent Application Publication No. 2007-290409 includes the hinge portion separately from the first thin portion of the leg piece, which requires another hinge portion for turnably retaining the door member while keeping the door member engaged, thus making it difficult to design the hinge portion.